regex - POSIX regular expression for showing line if contains a string -

If this is a special string then what is the regular expression to show the whole line?

The source string "ABC: I am your father" and I need to show everything on the line after "ABC": "So your end result is" I am your father ". < P>

^ ABC: [[space:]] (. *) < P> Input Text: ABC: I am your father

Matches:

  [0] => ABC: I am your father Am [1] = & gt; I am your father